The present invention relates to an electron beam lithography apparatus and more particularly to an electron beam lithography apparatus having an external magnetic field correcting device for correcting the rotational effect to an electron beam caused by the external magnetic field around the electron beam lithography apparatus.
The electron beam lithography apparatus is generally used for processing a semiconductor wafer. Recently, the integration capacity of the semiconductor device has become higher, and processing line width less than 0.5 .mu.m is needed. In this case, the positioning accuracy for positioning the electron beam in order to trace a lithographic pattern on the semiconductor wafer is needed to be less than 0.1 .mu.m. But it becomes impossible to keep the positioning accuracy less than 0.1 .mu.m, when the variation of the external magnetic field around the electron beam lithography apparatus is more than 5 mG.
In order to keep a high positioning accuracy, the electron beam lithography apparatus is covered with a high magnetic permeability material or is installed in a room covered by a high magnetic permeability material in order to shield the external magnetic field from the electron beam apparatus.
Further, in other prior art, the variation of the external magnetic field is detected so as to cancel it.
The Japanese Pat. Laid-open Nos. 52-136578 (1977) and 59-146144 (1984) are cited as examples of such systems.
But these conventional techniques have a problem of higher cost and it is difficult to perfectly cancel the variation of the external magnetic field.